(a) Technical Field
The present invention relates to a white LED device for illumination, and more particularly, to a white LED device for illumination with high color rendering properties using a blue LED chip having high luminance as an excitation light source.
(b) Background Art
With the commercialization of blue LEDs in the late 1990s, white LED devices have appeared, which employ a phosphor such as YAG (Yttrium Aluminum Garnet) for emitting yellow light by absorbing the excitation light at the corresponding wavelength using a blue LED chip as an excitation light source. This white LED has high luminance but is problematic because the wavelength interval between blue and yellow is wide, thus making it difficult to achieve mass production of white LEDs having the same color coordinates due to the scintillation effect by the color separation. Furthermore, it is very difficult to adjust color temperature (CT) and color rendering index (CRI), which are regarded as important in a light source for illumination. The CRI of typical white LEDs is only 75˜80.
Hence, white LED devices have been developed by applying an R/G/B multilayer fluorescent material on a UV LED chip to thus exhibit superior color stability and a wide emission spectrum as in incandescent bulbs. CT and CRI in such white LEDs are easy to adjust and thus white LEDs are receiving attention as a light source of an LED for illumination (Japanese Patent Application Publication No. 2002-171000). However, this patent is problematic because the white LED using the UV chip as an excitation light source has low luminance, compared to white LED devices using blue LED chips.
In addition, methods of emitting white light by combining multiple LED chips such as R/G/B have been proposed, but have drawbacks, such as non-uniform driving voltage per chip, and changes in the power of chips depending on the ambient temperature, which thus produces different color coordinates.
Although a variety of methods have been devised to achieve white LEDs as mentioned above, thorough research is ongoing into white LEDs using green and red phosphors instead of the yellow phosphor, with the use of a blue LED as an excitation light source due to high luminance of the blue LED (Korean Patent Application Publication No. 2008-0063709). In this case, color reproducibility may be increased to some extent, but is still insufficient. For example, a white LED lamp including green and red phosphors has low CRI for specific colors such as R9 (Red) or R12 (Blue).
Furthermore, because of instability of the material for the phosphor, such as damage to the red or green phosphor of the white LED device due to external energy or the like, unreliable products may result.